New enzyme immunoassays for sensitive detection of circulating Candida albicans mannan and antimannan antibodies: useful combined test for diagnosis of systemic candidiasis

Abstract

Two standardized enzyme immunoassays for the serological diagnosis of candidiasis were developed. The first one detects antimannan antibodies, while the second one detects mannan with a sensitivity of 0.1 ng/ml. These tests were applied to 162 serum samples retrospectively selected from 43 patients with mycologically and clinically proven candidiasis caused by Candida albicans. Forty-three serum samples were positive for mannan, and 63 had significant antibody levels. Strikingly, only five serum samples were simultaneously positive by both tests. When the results were analyzed per patient, 36 (84%) presented at least one serum positive by one test. For 30 of them, positivity by one test was always associated with negative results by the other test for any of the tested sera. For six patients whose sera were positive for either an antigen or an antibody response, a balance between positivity by each test was evidenced by kinetic analysis of sera drawn during the time course of the infection. Controls consisted of 98 serum samples from healthy individuals, 93 serum samples from patients hospitalized in intensive care units, and 39 serum samples from patients with deep mycoses. The sensitivities and specificities were 40 and 98% and 53 and 94% for mannanemia or antibody detection, respectively. These values reached 80 and 93%, respectively, when the results of both tests were combined. These observations, which clearly demonstrate a disparity between circulation of a given mannan catabolite and antimannan antibody response, suggest that use of both enzyme immunoassays may be useful for the routine diagnosis of candidiasis.

FIG. 1

EIA detection of anti-C. albicans mannan antibodies. The standard curve was obtained with serial dilutions of a pool of sera strongly reacting with mannan extracted from C. albicans VW32. Standard reactivity of 100 AU was determined as the dilution that gave the maximal absorbance at a λ of 450 nm.

FIG. 2

EIA detection of mannan extracted from C. albicans VW32 and spiked into a pool of negative sera. Standard deviations calculated from duplicates in three different experiments are noted by error bars.

FIG. 3

Mannanemia in relation to antimannan antibody titers in 162 serum samples from 43 patients with systemic candidiasis. Antimannan antibody titers (reported in AU) were divided into the following four categories: A, 0 to 10 AU; B, 10 to 20 AU; C, 20 to 40 AU; D, >40 AU.

FIG. 4

Examples of kinetic evolution of antigenemia (○) and antimannan antibody response (●) detected by EIA. Patients 39 (a) and 43 (b) had systemic candidiasis. The arrow marks the date of mycological isolation of C. albicans from blood and a drain. The curves are drawn by using the interpolate regression.